The invention relates generally to channeled fuel bundles for a nuclear reactor and, more particularly, to a shipping container enabling the shipment of a nuclear fuel bundle in a pre-channeled condition.
With reference to FIGS. 1 and 2, a typical fuel assembly in a light water boiling nuclear reactor vessel includes a lower tie plate 1, an upper tie plate 2 and a matrix of sealed fuel rods 3 supported between the upper and lower tie plates between fuel rod expansion springs 4 and finger springs 5 as shown. Spacers 12 serve to support the fuel rods 3 against lateral movement. The fuel rods 3 contain nuclear fuel pellets 6 in sealed containment for supporting a required critical reaction for the generation of steam. One or more coolant water rods 7 is included in the matrix of the fuel rods 3 and is also supported between the upper 2 and lower 1 tie plates. A channel 8 surrounds the tie plates, fuel rods and coolant water rods, and is secured via a channel fastener assembly 9 to the top of the fuel assembly via a compression channel fastener spring 14. In some cases the channel 8 may also be secured to both the lower tie plate 1 and the upper tie plate 2 within the same fuel assembly. The channel 8 is commonly square in cross-section and is made of metal (preferably an alloy called Zircaloy). A bail handle 10 is integrated within the upper tie plate 2 as part of the assembly for transporting and moving the fuel assembly.
In use, water passes from the bottom of the channeled fuel assembly to the top of the fuel assembly. Water enters through the lower tie plate 1 within the channel 8 and passes between the vertically standing fuel rods 3. Heated water and generated steam exit from within the channel 8 between the spacers 12 and fuel rods 3 and out through the upper tie plate 2. The channel 8 confines the required moderator coolant flow to a flow path that is restricted between the tie plates 1, 2.
The lower tie plate 1 and the upper tie plate 2 serve to support the sealed fuel rods 3 in the vertical and standing matrix. Typically, the upper tie plate 2 forms an overlying matrix of fuel rod support points, such as tie rods. Eight of these support points are conventionally placed corresponding with male threaded tie rods 11. The tie rods 11, which contain fuel pellets 6 similar to the fuel rods 3, are threaded at their lower and upper ends for corresponding attachment to the lower tie plate 1 and the upper tie plate 2. The lower tie plate 1 similarly forms an underlying matrix of fuel rod support points. These underlying support points correspond for the most part to the overlying support points of the upper tie plate 2. Conventionally, about eight of these support points are threaded with female apertures, which correspond to the overlying apertures in the upper tie plates 2. Into these threaded support points in the lower tie plates 1 are placed the lower threaded ends of the fuel tie rods 11. Thus, conventionally, the two tie plates 1, 2 are tied together with the fuel tie rods 11, by their threaded end plugs.
Currently, the fuel bundle, channel, and channel fastener are shipped to the customer site separately in different shipments. To ship the fuel bundles from the factory to the customers requires significant preparation including plastic inserts as support for each fuel rod, plastic sleeving to prevent foreign material from entering the length of the bundle, and protective netting to prevent debris from entering from the top or bottom of the fuel bundle. Two fuel bundles are typically loaded into a single NRC certified shipping package without channels.
Channels and channel fasteners are manufactured and shipped from a separate facility than the fuel bundle. The channels are currently packed and shipped to customers in custom single-use disposable shipping containers.
Once received at the customer site, the fuel is unloaded from the shipping packages one bundle at a time. The plastic inserts and protective netting are removed and placed back into the shipping package, and the materials are sent back to the fuel manufacturing facility for disposal.
The channels are received at the customer site and are removed from their single shipping container. Once removed from the shipping container, the protective vacuum-sealed sleeving is removed from each channel, prior to assembly. The channel container and their sleeving materials are then disposed of by the customer. The channel fasteners are shipped to the customer site in a separate container, and packing materials are disposed of separately.
Once each component has been independently inspected, the fuel bundle, channel, and channel fastener are assembled on site. To install the channel onto the fuel bundle, the channel must be oriented in the proper position and raised above the upper tie-plate and slowly lowered over each of the grid spacers until the channel engages the lower tie-plate. Depending on the fuel bundle design, the channel may interface with the finger springs attached to the lower tie-plate.
It would be desirable to provide a shipping container that would enable a fuel bundle to be shipped from the factory as a fully assembled channeled fuel bundle that is ready for placement within the reactor core vessel.